Using a polyol mixture comprising PBD for creating a PU-based artificial turf

ABSTRACT

Method of manufacturing an artificial turf includes: creating fluid polyurethane mass, the creation comprising reacting first and second polyols with an isocyanate, the first polyol being a polyether polyol and/or a polyester polyol having at least 2 hydroxyl groups per molecule, the second polyol being polybutadiendiol; the isocyanate comprising isocyanate monomers, isocyanate polymers or isocyanate prepolymers or a mixture thereof, the isocyanate monomers, isocyanate polymers and the isocyanate prepolymers having two or more isocyanate groups per molecule; incorporating an artificial turf fiber into a carrier such that a first portion of the fiber protrudes to the front side of the carrier and that a second portion of the fiber is located at the back side of the carrier; and adding the fluid polyurethane mass on the back side of the carrier; and hardening the fluid polyurethane mass.

FIELD OF THE INVENTION

The invention relates to artificial turf and the production of artificial turf which is also referred to as synthetic turf.

BACKGROUND AND RELATED ART

Artificial turf or artificial grass is surface that is made up of fibers which is used to replace grass. The structure of the artificial turf is designed such that the artificial turf has an appearance which resembles grass. Typically artificial turf is used as a surface for sports such as soccer, American football, rugby, tennis, golf, for playing fields, or exercise fields. Furthermore artificial turf is frequently used for landscaping applications.

Artificial turf fields are brushed regularly to help fibers stand-up after being stepped down during the play or exercise. Throughout the typical usage time of 5-15 years it may be beneficial if an artificial turf sports field can withstand high mechanical wear, can resist UV, can withstand thermal cycling or thermal ageing, can resist inter-actions with chemicals and various environmental conditions. It is therefore beneficial if the artificial turf has a long usable life, is durable, and keeps its playing and surface characteristics as well as appearance throughout its usage time.

US 2009/0275690 A1 describes a method for promoting adhesion between an apolar material, e.g. polyethylene and a polar material, e.g. polyurethane. Adhesion to an apolar material is promoted by creating a blend of a non-polar polyolefin and a polydiene-based polyurethane. A polymer blend is a material analogous to metal alloys, in which at least two polymers are blended together to create a new material with different physical properties. In this purely “physical” mixture no new chemical bonds between the macromolecules of the two or more different polymers are created.

It may be desirable to manufacture artificial turf fibers having a set of desired properties e.g. in respect to smoothness, tensile strength, resistance to shear forces, and/or resistance to splicing of fibers.

SUMMARY

The invention provides for a method of manufacturing artificial turf in the independent claims. Embodiments are given in the dependent claims. Embodiments can freely be combined with each other if they are not mutually exclusive.

In one aspect, the invention relates to a method of manufacturing artificial turf. The method comprises:

-   -   Creating fluid polyurethane mass, the creation comprising         reacting first and second polyols with an isocyanate,         -   the first polyol being polyether polyol and/or polyester             polyol having at least 2 hydroxyl groups per molecule, and             the second polyol being polybutadiendiol;         -   the isocyanate comprising isocyanate monomers, isocyanate             polymers or isocyanate prepolymers or a mixture thereof, the             isocyanate monomers, isocyanate polymers and the isocyanate             prepolymers having two or more isocyanate groups per             molecule;     -   incorporating an artificial turf fiber into a carrier such that         a first portion of the fiber protrudes to the front side of the         carrier and that a second portion of the fiber is located at the         back side of the carrier; and     -   adding the fluid polyurethane mass on the back side of the         carrier, the polyurethane mass thereby incorporating at least         the second portions of the fiber; and     -   hardening the fluid polyurethane mass on the back side of the         carrier.

Said particular way of creating artificial turf with a polyurethane (PU)-based backing may be advantageous as this type of backing material may be capable of fixing hydrophobic polyolefin fibers more firmly and more reliably. Many polymers used for producing artificial turf fibers, e.g. polyethylene, are hydrophobic. To the contrary, polyurethane is a hydrophilic material. As a consequence, Van-der-Waals forces between the fibers and the PU backing are weak and fibers may easily be pulled out of a PU backing when a tuft-withdrawal force is applied. By adding polybutadiendiol (PBD) in the reaction mixture used for creating the PU in a polyaddition reaction, the PU is made more hydrophobic and the attachment of the PU to the fiber via Van-der-Waals forces is increased. In the polyaddition reaction, the PBD acts as a hydrophobic polyol that increases hydrophobicity of the PU. The resulting PU be more hydrophobic than a standard PU and will attach more strongly to a polyethylene surface or fiber. The new PU variant is used for the production of artificial turf capable of strongly fixing individual monofilaments, fibers made of multiple monofilaments or tapes made of hydrophobic material, e.g. PE, in the backing.

In a further beneficial aspect, the creation of the PU-based backing according to embodiments of the invention may be advantageous as said type of backing is better protected against the effects of water. Applicant has observed that water, e.g. rain falling on artificial lawn of a sports field, may act as a softening agent in respect to PU. If PU is contacted with water, the water softens the PU and causes the PU to swell. The swelling may cause the destruction of the mechanical fixing of the fibers both in polyester-based as well as in polyether-based PU. Moreover, the contact with water may chemically destroy polyester-based PU by saponification which may also result in the destruction of the mechanical fixing of the fibers in the PU backing. Thus, in a further aspect, embodiments of the invention relate to a method for providing a hydrolytically stable form of PU that does neither swell nor saponificate significantly when exposed to water and water-based liquids.

Thus, according to embodiments, the polybutadiendiol is added to the polyols or to a reaction mixture comprising the polyols and the isocyanate for increasing the hydrophobicity of the PU and/or for creating a hydrolytically stable form of PU, i.e., a PU that does neither swell nor saponificate when exposed to water and/or for strongly mechanically fixing hydrophobic polyolefin fibers incorporated at least partially in the PU backing.

In a further beneficial aspect, chemical bonds between the PBD and the polyisocyanates are created, thereby preventing any delamination effect that may occur if hydrophilic and hydrophobic substances are combined in a single blend. The reaction that creates the chemical bonds is a polyaddition reaction whereby the first polyol as well as the PBD respectively react with the isocyanate to form polyurethanes.

According to embodiments, the isocyanate is a diisocyanate.

According to embodiments, the at least two hydroxyl groups per molecule of the first polyol are two terminal hydroxyl groups.

According to embodiments, the polybutadiendiol has an amount of 0.5-10% by weight of a combination of the first polyol (i.e., the polyester-polyol or the polyether-polyol) and the isocyanate. According to some of said embodiments, the polybutadiendiol has an amount of 1.0-9% by weight of said combination and preferentially has an amount of 4.0-8.0% by weight of said combination.

Said features may be beneficial as it has been observed that this PBD concentration generates a PU backing that fixes polyolefin fibers embedded therein so strongly that a so-called “stick-slips effect” occurs, in particular when using highly hydrophobic monofilaments, e.g. PE-monofilaments: a stick-slip effect describes a particular form of relative movement of two surfaces (e.g. a PE-fiber surface and the PU-surface surrounding said fiber), whereby the movement of the surfaces alternates between sticking to each other and sliding over each other, with a corresponding change in the force of friction. Typically, the static friction coefficient (a heuristic number) between two surfaces is larger than the kinetic friction coefficient. If an applied force is large enough to overcome the static friction, then the reduction of the friction to the kinetic friction can cause a sudden jump in the velocity of the movement. Typically, the stick-slip effect is considered as an unwanted effect, e.g. in respect to the relative movement of human skin and a PE fiber as in this context the risk of injuries and skin burns may be increased. However, applicant has surprisingly observed that the stick-slip effect in the context of PE/PU surface movements is a desirable and useful effect as it increases the resistance of the fiber to tuft withdrawal forces. Even in case a pulling force is high enough to pull a fiber some distance out of the backing, the stick-slip effect will cause the fiber to halt again, thereby causing the static friction coefficient rather the kinetic friction coefficient to take effect.

Thus, according to a further beneficial aspect of the invention, a PU-based artificial turf backing is provided that mechanically fixes hydrophobic polyolefin fibers or monofilaments, in particular PE-based fibers and monofilaments, particularly well by showing the stick-slip effect.

In particular when the PBD is added to the reaction mix in the most preferred concentration range of 2.0-4.0% by weight of a combination of the first polyol and the isocyanate, e.g. 3% by weight of said combination, the artificial turf fibers are sometimes fixed so firmly in the PU backing that the fiber will in many cases be break and torn apart rather than be pulled out of the backing.

Both the polyether-polyol and the polyester-polyol may consist of a single type of polyol or of a mixture of different types of polyols. Depending on the embodiment, the PBD and the first polyol can be added to the reaction mixture separately or can be contained in a single mixture that is mixed with the isocyanate.

According to embodiments, the first polyol is free of any PBD and hydrated PBD. In other words, the first polyol consists of one or more non-PBD-polyols.

According to embodiments, the first polyol is preferably a polyether polyol.

According to embodiments, the first polyol is preferably selected from a group comprising: a polycarbonate polyol, a polycaprolactone polyol, a propylene oxide based polyol, a polypropylene polyol, a polysulfide polyol, a polyether glycol like polytetramethylene ether glycol (PTMEG) or a mixture of one or more of said polyols. A “propylene oxide based polyol” may be generated from a monomer mix consisting of or comprising a propylene oxide monomer.

In a further embodiment, the first polyol is a mixture of one or more of the aforementioned polyetherpolyols together with a di- or tri-glycol having a hydroxyl value ranging from 400-2000 mg KOH/g. Preferentially, said di- or tri-glycoles are short chain di- or tri-glycoles. For example, the di- or tri-glycoles can be one or more of: diethylene glycole, dipropylene glycole, methyleneglycole, propyleneglycole, butyleneglycole. Adding the di- or tri-glycols may be advantageous as the crosslinking-density in the PU may be increased.

In further embodiments the first polyol comprises or consists of a mixture of a polyether polyol and a polyester polyol. Said polyester polyol can be, for example, vegetable oil based polyols as e.g. a castor oil based polyol as e.g. Desmophen 1150 or soya bean oil based polyols or gained from a re-esterification process.

According to embodiments, the first polyol has a number average molecular weight in the range of 500-6000 g/mol, more preferentially between 1.500 and 4.000 g/mol.

The number average molecular weight, Mn, is the total weight of all the polymer molecules in a sample, divided by the total number of polymer molecules in the sample.

According to embodiments, the polyether polyols is a bifunctional polyether polyol having a hydroxyl value of about 50-60 mg KOH/g. According to another example, a bifunctional polyether polyol having a hydroxyl number of about 26-30 mg KOH/g can be used, e.g. a polyol based on propylene oxide having a number average molecular weight of about 4000 g/mol. However, it is also possible to use polyether polyols having a lower or even higher molecular weight.

According to embodiments, the polybutadiendiol has a number average molecular weight in the range of 1000-6000 g/mol, more preferentially between 1.500 and 4.500 g/mol.

According to preferred embodiments, the polybutadiendiol is a hydrogenated polybutadiendiol. Using hydrogenated PBD may provide for an increased chemical stability of the generated PU. In particular, the saturated nature of the hydrogenated PBD provides light and weather stability, prevent the PU backing becoming yellow or lose its mechanical properties such as flexibility, elongation, and strength.

For example, a hydrogenated polybutadiendiol having a number average molecular weight of about 2000 g/mol whose double bonds have been fully (>97%) hydrogenated, the hydroxyl units being retained, can be used as the PBD that is added to the reaction mix. According to another example, a polybutadiendiol having a number average molecular weight of about 3000 g/mol can be used as the PBD that is added to the reaction mix.

According to embodiments, the method further comprises adding a wetting agent to a mixture comprising the first and/or second polyols and/or the isocyanate.

Adding a wetting agent to the reaction mixture for creating the PU mass may be advantageous as the wetting agent reduces the surface tension and helps the PU mass to wet the carrier (that can be, for example, a hydrophobic polyolefin-based textile) and/or to wet the monofilaments and fibers incorporated at least partially in the PU backing. Wetting monofilaments is a particularly demanding task for fixing tufted bundles of PE monofilaments in a PU coated backing. This is because monofilament tuft bundles are often aligned very close to each other, thereby prohibiting any PU liquid or PU foam to invade the space within a tufted monofilament bundle.

Using a wetting agent may be advantageous as the PBD has been observed to increase the viscosity of the liquid PU mass compared to the PU created from the same reaction mixture but lacking PBD. It has been observed that the wetting of the carrier textile and/or the wetting of the fibers is reduced by an increase of PU-viscosity. Using the wetting agent compensates for this effect, thereby allowing to increase the hydrophobicity without negatively affecting the wetting of the fibers.

In a further beneficial aspect, the wetting agent allows using higher PBD amounts and thus generating a more hydrophobic PU as the wetting agent compensates for the increased viscosity.

According to embodiments, the wetting agent is a surfactant having an amount of 0.01% to 1.0% by weight of a combination of the first and second polyols and the isocyanate, more preferentially an amount of 0.8%-1.2% by weight of said combination and most preferentially an amount of 0.05-0.15% by weight of said combination.

Said surfactant concentration is typically not high enough for strong foam generation and for controlling the density and volume of the PU foam applied on the backside of an artificial turf backing carrier. However, as the surfactant according to embodiments of the invention is not added for creating foam but rather as a wetting agent, the above mentioned concentration ranges are preferable.

The “backside” of the carrier as used herein is the side opposite to the side from which the larger portions of the fibers emanate.

“Surfactants” as used herein are compounds that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid. Surfactants may be, for example, amphiphilic substances, in particular organic amphiphilic substances which contain both hydrophobic groups and hydrophilic groups. Therefore, a surfactant contains both a water-insoluble (or oil-soluble) component and a water-soluble component. Surfactants will diffuse in an the liquid PU mass and will adsorb at interfaces between the PU mass and the hydrophobic monofilaments and/or the hydrophobic carrier of the backing. A surfactant may be, for example, a hydrocarbon surfactant such as, for example, Triton X-100, or, more preferentially, a fluorosurfactant or a mixture of hydrocarbon surfactant and a fluorosurfactant. Fluorosurfactants have a hydrophobic tail in the form of a straight chain fluorocarbon and a polar portion. Fluorosurfactants are particularly stable, also in harsh thermal and/or chemical environments.

According to embodiments, the method comprises adding a pale oil to the a mixture comprising the polyols and/or comprising the isocyanate. The pale oil is added in an amount of 0.5% to 4%, more preferentially 0.7% to 1.2% by weight of a combination of the polyols and the isocyanate.

“Pale oils” or “white oils” as used herein are highly refined mineral oils that are only lightly colored or colorless and that are chemically inert. Preferentially, the pale oils used for embodiments of the invention are also pure, stable, odorless and non-toxic. The term “white oil” is a misnomer, in that white oils are not white, but crystal clear. Pale oils can be produced from a variety of substances, depending on the process used. For example, naphthenic oils and some mineral oils can be used as pale oils.

For instance, light colored, non-staining naphthenic oils refined from specially selected wax-free crude through the use of severe hydrogenation can be used, e.g. PALE OIL 40-NYTEX 5130 of NYNAS.

Adding pale oil may further reduce the viscosity of the liquid polymer mass, thereby increasing the wetting of the carrier and/or the artificial turf monomers and fibers and increasing the strength of the mechanical fixing.

According to embodiments, the method further comprises adding a catalyst to the polyols or to the isocyanate or to a reaction mixture comprising the same.

According to embodiments, the fluid polyurethane mass has a density of more than 1000 g/l, preferentially having a density in the range of 1100 g/l-1500 g/l, more preferentially in a range of 1200 g/l-1400 g/l. The first polyol and/or the catalyst may be chosen such that the density of the generated PU mass is in at least one of the specified density ranges. Said density ranges have been observed to provide PU-based artificial turf backings that can be easily laid without bulging, that is elastic and robust against various pulling, pushing and shear forces.

According to some embodiments, the liquid PU mass is a non-foam polyurethane, i.e., a PU that is (substantially) non-porous.

Foams and fluids in this high density range are often highly viscous and often do not wet fibers and in particular monofilaments within monofilament bundles appropriately. However, by using a more hydrophobic PU form, optionally further comprising a wetting agent, also PU masses having the above mentioned high density can be used for firmly fixing PE filaments by Van-der-Waals forces. Thus, embodiments of the invention may allow to firmly fix hydrophobic fibers also in a high-density PU backing.

According to embodiments, incorporating the artificial turf fiber into the carrier comprises: tufting the artificial turf fiber into the carrier. According to alternative embodiments, incorporating the artificial turf fiber into the carrier comprises weaving the artificial turf fiber into the carrier.

According to embodiments, the artificial turf fiber is a bundle of monofilaments. In this context, using a more hydrophobic PU version, optionally in combination with a wetting agent, is particularly advantageous as standard PU foams and fluids usually are not able to wet the monofilaments located at the inside of a monofilament bundle. By wetting also the monofilaments inside said bundles, the mechanical fixing is significantly increased.

According to embodiments, the artificial turf fiber is a hydrophobic polyolefin fiber, e.g. a polyethylene (PE) fiber, a polypropylene (PP) fiber, a polybutylene fiber or a fiber consisting of a polymer blend comprising a hydrophobic polyolefin as main component.

Depending on the embodiment, the hardening process may be performed passively, e.g. by incubating the liquid PU mass applied and dispersed on the back side of the carrier at room temperature, or by heating the PU backing for a given time to temperature significantly above room temperature.

According to some embodiments, the hardening of the fluid polyurethane mass comprises heating the polyurethane mass having been applied and dispersed on the back side of the carrier to a temperature of 70-140° C. For instance, the heat is applied for a time period of 1-5 minutes, preferentially 2-3 minutes.

The hardening process, also referred to as “curing” process, is performed to let the residual liquids leave the PU mass so that the PU mass hardens and develops its strength. The hardened PU mass on the backing will tightly enclose the portions of the fibers having been incorporated in the fluid polyurethane mass.

According to embodiments, the method further comprises generating the polymer fiber. The generation comprises:

-   -   generating a polymer mixture;     -   extruding the polymer mixture into a monofilament;     -   quenching the monofilament;     -   reheating the monofilament;     -   stretching the reheated monofilament to form the monofilament         into the artificial turf fiber.

In a further aspect, the invention relates to an artificial turf manufactured according to the method for generating a PU-based artificial turf according to any one of the embodiments described herein.

In a further aspect, the invention relates to artificial turf comprising a polyurethane backing. The polyurethane is the reaction product of first and second polyols with an isocyanate. The first polyol is polyether polyol and/or polyester polyol having at least 2 hydroxyl groups per molecule. The second polyol is polybutadiendiol. The isocyanate comprises isocyanate monomers, isocyanate polymers or isocyanate prepolymers or a mixture thereof. The isocyanate monomers, isocyanate polymers and the isocyanate prepolymers have two or more isocyanate groups per molecule.

The artificial turf further comprises a carrier and an artificial turf fiber incorporated into the carrier such that a first portion of the fiber protrudes to the front side of the carrier and that a second portion of the fiber is located at the back side of the carrier, at least the second portion of the fiber being incorporated into the polyurethane backing.

It is understood that one or more of the aforementioned embodiments of the invention may be combined as long as the combined embodiments are not mutually exclusive.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention are explained in greater detail, by way of example only, making reference to the drawings in which:

FIG. 1 shows a flow chart of a method of manufacturing a PU-based artificial turf;

FIG. 2 shows multiple tanks and mixers comprising educts and the reaction mixture for creating PU;

FIG. 3 shows a “knife over roll” PU-coating process;

FIG. 4 illustrates the extrusion of the polymer mixture into a monofilament;

FIG. 5 shows the tufting of an artificial turf fiber and illustrates first and second parts of the fiber;

FIGS. 5a-5b shows the tufting of an artificial turf fiber and illustrates first and second parts of the fiber; and

FIGS. 6a-6b shows portions of monofilaments and fibers embedded in the PU backing.

FIG. 6 shows portions of monofilaments and fibers embedded in the PU backing.

DETAILED DESCRIPTION

Like numbered elements in these figures are either equivalent elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is equivalent.

FIG. 1 shows a flow chart of a method of manufacturing a PU-based artificial turf backing 602 as shown, for example, in FIG. 6. In a first step 102, a fluid polyurethane mass 210 is created as depicted, for example, in FIG. 2. The creation of the liquid PU mass comprises reacting first and second polyols with an isocyanate. The first polyol is a polyether polyol or a polyester polyol or a mixture thereof, and the second polyol is polybutadiendiol. The polyether and/or polyester polyol have two hydroxyl groups per molecule.

Polyether polyols are made by reacting epoxides like ethylene oxide or propylene oxide with the multifunctional initiator in the presence of a catalyst, often a strong base such as potassium hydroxide or a double metal cyanide catalyst such as zinc hexacyanocobaltate-t-butanol complex. Common polyether polyols are polyethylene glycol, polypropylene glycol, and poly(tetramethylene ether) glycol.

Polyesters are formed by condensation or step-growth polymerization of polyols and dicarboxylic acids (or their derivatives), for example diethylene glycol reacting with phthalic acid. Alternatively, the hydroxyl group and the carboxylic acid (or their derivatives) may be within the same molecule, as in the case of caprolactone. Polyether polyols and/or polyester polyols can be bought ready-made from various suppliers.

The isocyanate comprises isocyanate monomers, isocyanate polymers or isocyanate prepolymers or a mixture of isocyanate monomers, isocyanate polymers and isocyanate prepolymers. The isocyanate monomers, polymers and prepolymers have two or more isocyanate groups per molecule.

For example, the isocyanate can be methylene diphenyl diisocyanate (“MDI”). MDI is an aromatic diisocyanate. It exists in three isomers, 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI. Embodiments of the invention may be based on any of said isomers, preferentially the 4,4′ isomer is used as the isocyanate. MDI reacts with the polyols (i.e., with the PBD and the polyether polyol or the polyester polyol) in the manufacture of the PU mass.

In step 104, one or more turf fibers are incorporated into a carrier, e.g. a textile or other material comprising perforations. For example, the incorporation may comprise weaving, spinning, twisting, rewinding, and/or bundling the a monofilament, e.g. a stretched monofilament, into the artificial turf fiber and than incorporating the fiber into the carrier. This technique of manufacturing artificial turf is known e.g. from United States patent application US 20120125474 A1.

In step 106, the liquid PU mass generated in step 102 is added on the backside of the backside of the carrier (see e.g. FIG. 3). Thereby, the fibers, including the monofilaments within bundled fibers, and the carrier material are wetted by the liquid PU mass.

In step 108, the liquid PU mass solidifies into a solid PU-based artificial turf backing that strongly fixes hydrophobic fibers without the need to create chemical bonds between the PU backing and the fiber material. For example, the PU mass on the backside of the carrier may be hardened at room temperature or in an oven.

FIG. 2 shows multiple tanks and mixers comprising educts and the reaction mixture for creating PU.

A first mixing unit is used for creating a first mixture comprising the polyether polyol or the polyester polyol (but not the hydrated PBD). For example, the first mixture comprises a polyether-polyol, e.g. a polyether-polyol having a number average molecular weight of about 4000 g/mol, e.g. a polyol based on polymerized propyleneoxide. The polyether polyol may be obtained e.g. in the form of a ready-made polyol.

Optionally, the first mixture comprises filler materials. Adding a filler may reduce cost and/or help to achieve a particular look or weight. Fillers can be, for example selected from the group ground limestone, precipitated calcium carbonate, china clay, cold fly ash, silicates and other inert material including non-reactive liquids. Moreover fillers with flame retardant and/or intumescent efficiency like aluminium trihydroxide or ammonium polyphosphate can be used or mixtures of the aforementioned fillers.

Moreover, the first mixture may comprise a catalyst for boosting the polyaddition reaction that generates the PU. The catalyst can be, for example, amine compounds and metal-organo complexes. Traditional amine catalysts have been tertiary amines such as triethylenediamine (TEDA, 1,4-diazabicyclo[2.2.2]octane or DABCO), dimethylcyclohexylamine (DMCHA), and dimethylethanolamine (DMEA).

Metal-organo complexes used as polyurethane catalysts can be based e.g. on mercury (e.g. mercury carboxylates), lead, tin (e.g. alkyl tin carboxylates and oxides), bismuth, and zinc (e.g. bismuth and zinc carboxylates).

The first mixture is then stored in a first tank 202, e.g. a day tank, i.e., a tank sized to provide a day's worth of usage.

The second mixture, i.e., the isocyanate monomer/polymer/prepolymers mixture, e.g. MDI, is stored in a second tank 204 that is preferentially also a day tank.

A further container 206 that is typically of a smaller size than the first and second tank comprises a third substance mixture. The third substance mixture comprises the PBD and optionally further substances such as a wetting agent, pale oil and/or one or more further additives. The one or more further additives can be, for example, flame retardants, pigments, extenders, cross linkers, blowing agents etc. The container 206 may be part of or coupled to a blender 208. The blender 208 receives the first mixture from the first container, receives the second mixture from the second container 204 and receives the PBD and the one or more optional substances (wetting agent, pale oil and/or further additives) from the further container 206. The blender 208 blends the first, second and third mixtures received from respective tanks and containers in amounts suited to generate a reaction mixture 210 whose substance concentrations are within the ranges specified herein for embodiments of the invention. For example, the first, second and third mixtures are blended such that the number of OH groups in the first polyol molecules in the first mixture in combination with the number of OH groups in the PBD molecules in the third mixture will roughly correspond (e.g. in a range of ratios ranging from “0.9:1” to “1:0.9”) to the number of NCO groups in the isocyanate molecules (monomers and prepolymers). The third mixture is added by the blender 208 to the reaction mixture 210 in such an amount that the PBD in the reaction mixture has a concentration range of 0.5-5% by weight of a combination of the first polyol and the isocyanate.

An example of a third mixture is given below:

% by weight of the third Description mixture in container 206 Hydrogenated hydroxyl-terminated 56% polybutadien (PBD): Conductivity additive & pigments 16% Pale oil 28%

The third mixture will be blended with the first and second mixture such that the PBD is contained in the reaction mixture/liquid PU mass in an amount of 0.5-5% of a combination of the first polyol and the isocyanate.

According to embodiments, the first and second mixtures in the first and second tanks are supplied as “two pack systems” or “two component systems” wherein the polyol part acts as the first mixture in the first tank and the polyisocyanates part acts as the second mixture in the second tank. While the first and second mixtures may be bought as ready-made two-component PU-generation systems, the third mixture in container 206 may be customized to specific needs of a customer, e.g. by adding a certain pigment to achieve a desired coloring effect or by adding a certain amount of PBD and/or oil and wetting agent in order to achieve a desired viscosity given a desired PU-density.

The blender 208 may be a low-pressure gear pump, which produce a desired mixing ration of the first, second and third mixtures. Ratio and material distribution are driven by a computer assisted equipment. Despite the viscosity of the PU mass 210, the PU mass penetrates deeply into the tufts of artificial grass, and wets the textile carrier and the monofilaments contained therein.

The reaction mixture 210 generated by the blender 208 is output to a container 212 that may have the form of a hose. The chamber 212 has an opening 214 that leads to a coater, e.g. a “knife over roll” coating assembly as depicted, for example, in FIG. 3. Typically, the reaction mixture output by the blender 208 reaches the opening 214 being part of the coating assembly within 30 seconds. At this point, the polyaddition reactions resulting in the generation of the liquid PU mass used for coating a carrier textile of a piece of artificial turf will largely have completed already, but some reactions may still continue during the coating process.

According to embodiments, the first polyol(s), the PBD and the isocyanate in total constitute at least 25%, according to other embodiments at least 40%, or even more than 95% of the total amount of the total reaction mix used for generating the liquid PU mass that—after a curing process—is used as the artificial turf backing. This means that the totality of fillers, wetting agents, pale oils and any further additives (e.g. extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and so on) typically constitutes less than 75%, or less than 60%, or in further embodiments less than 5% by weight of the reaction mix used for generating the PU. An example would be a reaction mixture comprising about 20% isocyanate, 4% PBD, 20% first polyol, 2% catalyst, 3% additives like oils, dyes or flame retardants, and 51% filler material. In some example embodiments the reaction mixture does not comprise any filler material.

According to preferred embodiments, the liquid PU mass is a non-foam polyurethane, i.e., a PU that is (substantially) non-porous.

Polyols or polyhydroxylated compounds are known to absorb water and generally are the source for the introduction of water into the formulation. Moisture is introduced either in the polyhydroxylated compound or in some other ingredient, and this moisture can react with the isocyanate to produce urea linkages and carbon dioxide. The urea linkages are strong and desirable; however, the carbon dioxide causes bubbles to appear in the product. In many cases, the presence of bubbles in the product weakens the structure of the PU backing. Therefore, according to embodiments of the invention, the reaction conditions and educts are chosen such that a non-foamed liquid PU mass 210 is generated. The generation of “non-foamed” liquid PU masses is described, for example, in “Polyurethanes: Science, Technology, Markets, and Trends”, Mark F. Sonnenschein, ISBN: 978-1-118-73791-0.

FIG. 3 shows a “knife over roll” PU-coating process and a corresponding coating assembly. The liquid, viscous reaction mix 210, which is also referred to as liquid PU mass upon leaving the opening 214 of the container 212, is applied on a carrier structure 308. A plurality of artificial turf fibers 302 protrude from the front side of the carrier structure and the liquid PU mass 210 is applied on the back side of the carrier. The PU mass is applied continuously while a roll 306 causes the carrier 308 to move in a direction indicated by the arrows. A “knife” 304 shown in cross section view is located at a defined distance above the carrier 308 and ensures that the viscous PU mass 210 passing the space between the knife 304 and the carrier 308 has a defined height.

According to preferred embodiments, the liquid PU mass is a non-foam polyurethane, i.e., a PU that is (substantially) non-porous.

The high viscosity of the PU mass according to embodiments of the invention and the configuration and dimensions of the opening 214 and the speed of the PU mass flow through this opening are chosen such that a defined amount of PU mass builds up and accumulates in front of the front side of the knife 304. This ensures that the thickness of the PU backing of the generated piece of artificial turf is constant.

After the PU mass 210 was homogeneously applied on the back side of the carrier 308, it is hardened (increase of viscosity) by keeping the coated piece of artificial turf for about 10 minutes at room temperature. Typically, the PU backing is solid 30 minutes after its application on the carrier.

Preferentially, in order to sped up the solidification, the artificial turf is exposed to elevated temperatures around 100° C. Typically, after 90 seconds at elevated temperature, 90 to 95% of the PU mass is “cured” (is in solid state). For example, the coating assembly may automatically transport the coated piece of artificial turf in an oven.

FIG. 4 illustrates a liquid polymer mixture 400. The polymer is a polyolefin, e.g. a polyethylene mixture. The polymer mixture is used for producing a monofilament 412 in an extrusion process. The polymer mixture 400 comprises additives 404, 406 such as UV-stabilizers, pigments, flame retardants or the like. A screw, piston or other device is used to force the polymer mixture 400 through a hole 410 in a plate 408. This causes the polymer mixture 400 to be extruded into a monofilament 412. In some embodiments, the polymer mixture may comprise polymer beads 408 of a more rigid polymer, e.g. polyamide. Due to flow dynamics during the extrusion process, the beads will tend to concentrate in the center of the monofilament 412. This may lead to a concentration of rigid, thread-like PA regions in the core region of the monofilament while the surface of the monofilament almost completely consists of the hydrophobic PE. Thus, a fiber with increased resilience is provided which has a soft PE surface that protects against injuries and skin burns which, however, has a very hydrophobic surface and may therefore easily detach from a polar PU backing.

Thus, the monofilament is produced by feeding the polymer mixture 400 into an fiber producing extrusion line. The melt mixture is passing the extrusion tool, i.e., a spinneret plate or a wide slot nozzle, forming the melt flow into a filament or tape form, is quenched or cooled in a water spin bath, dried and stretched by passing rotating heated godets with different rotational speed and/or a heating oven. The monofilament or fiber may later be annealed online in a second step passing a further heating oven and/or set of heated godets.

According to embodiments, manufacturing an artificial turf fiber (which may comprise one or more monofilaments 412) comprises forming the stretched monofilament into a yarn. Multiple, for example 4 to 8 monofilaments, could be formed or finished into a yarn.

According to embodiments, the extrusion is performed at a pressure of 40-140 bars, more preferentially between 60-100 bars. The polymer mixture may be created by adding polymer granules to a solid polymer composition that is mixed and heated until all polymers are molten. For example, the polymer mixture may be heated to reach at the time of extrusion a temperature of 190-260° C., more preferentially 210-250° C.

According to embodiments, the stretching comprises stretching the reheated monofilament according to a stretch factor in the range of 1.1-8, more preferentially in the range of 3-7.

According to embodiments, the quenching is performed in a quenching solution having a temperature of 10-60° C., more preferentially between 25° C.-45° C.

According to embodiments, the incorporation of the artificial turf fiber into the carrier comprises tufting or weaving the artificial turf fiber into the carrier.

According to embodiments, the quenching solution, e.g. a water bath, has a temperature (right after the extrusion nozzle or hole(s)) of 10-60° C., more preferentially between 25° C.-45° C., and even more preferentially between 32° C.-40° C.

According to embodiments, the extrusion is performed at a pressure of 80 bar, the polymer mixture at time of extrusion has a temperature of 230° C., the stretch factor is 5 and the quenching solution, e.g. a water bath, has a temperature of 35° C.

FIG. 5a shows the tufting of an artificial turf fiber and how a plurality of artificial turf fibers can be arranged in a carrier 308, e.g. a textile plane, by means of tufting. The carrier 308 may be a textile made of a hydrophobic polymer, e.g. PE. Tufting is a type of textile weaving in which an artificial tuft fiber 501 (that may be a monofilament 412 or a bundle of multiple monofilaments) is inserted on a carrier 308.

A “monofilament” as used herein is a filament generated by extruding a liquid polymer mixture through a single opening or is a slice of a polymer tape generated in accordance with the slit film technique.

After the inserting is done, as depicted in FIG. 5a , short U-shaped loops of the fiber point outside of the carrier's surface. Then, one or more blades cut 502 through the loops. As a result of the cutting step, two artificial turf fiber ends per loop and monofilament point out from the carrier and a grass-like artificial turf surface is generated as depicted in FIG. 5b . Thereby, first portions 506 of the monofilaments (corresponding to first portions of the artificial turf fibers) which have been inserted in the carrier 308 are exposed to a bottom side (back side) of the carrier and second portions 302 of said monofilaments are exposed to a top side of the carrier. Some portions 504 of the monofilaments/fibers are located within the carrier structure. Fibers or fiber bundles may protrude in loops 503 outside of the back side of the carrier. The piece of artificial turf generated in the tufting process may be forwarded to the coating assembly depicted in FIG. 3 for applying the PU mass 210 on the back side of the carrier.

FIGS. 6a and 6b show portions of monofilaments and fibers which are embedded in the PU backing. Reference number 600 refers to the total height of a piece of artificial turf having been coated with the PU mass 210 generated according to embodiments of the invention. The hydrophobized PU mass may optionally contain pale oil and a surfactant in liquid or fluid state has flown around and wetted the fibers, including the monofilaments located in the inside of a fiber consisting of a plurality of monofilaments. The PU mass 210′ depicted in FIGS. 6a and 6b has already solidified and strongly fixes the hydrophobic polymer monofilaments in the PU backing.

FIGS. 6a and 6b correspond to different embodiments of the invention.

FIG. 6a shows a piece of artificial turf made from a highly viscous PU mass and/or with a close meshed carrier 308 that prevents the PU mass from penetrating and transgressing the carrier. In this embodiment, first portions 302 of the filaments 501 protrude from the carrier 308 to the front side of the artificial turf and are not embedded in a PU film as the liquid PU mass 210 was not able to reach the front side of the carrier during the coating process. Also the fiber portions 504 within the carrier are not wetted by the PU mass in this embodiment. However, second parts 506 of the monofilaments were embedded in the liquid PU mass 210 during the coating process. Although the length of said second portions is comparatively small, the high hydrophobicity and the improved wetting of the fibers by the PU mass 210 ensure that the fibers are firmly fixed by Van-der-Waals forces in the backing and that a slip stick effect further protects the fibers against tuft withdrawal forces.

FIG. 6b shows a piece of artificial turf made from a less viscous PU mass (compared to the embodiment of FIG. 6a ) and/or with a wide-meshed carrier 308. The carrier may be a textile mesh or another type of material that comprises perforations that allow the PU mass 210 to penetrate the carrier and reach the front side of the artificial turf. Thus, portion 302 of the fibers in FIG. 6b comprises a first portion 604 which is not embedded in the PU film 210 and another portion 602 which is embedded in the PU film 210.2 having penetrated the carrier. In addition, portions 504 and 506 are wetted by and are embedded in the liquid PU mass 210. Thus, the carrier, portions of the fibers inserted in the carrier and further portions 602 of the fibers at the front side of the carrier may become embedded in the PU backing in addition to the portions 506 on the backside of the carrier.

The liquid PU mass 210 added in the coating process on the backside of the carrier surrounds and thereby mechanically fixes at least some portions of the monofilaments of the arranged artificial turf fibers. Then, the liquid PU mixture 210 solidifies into a PU-based artificial turf backing 210′ at room temperature or in an oven. The solid film acts as the artificial turf backing. In some examples, additional coating layers may be added on the bottom of the artificial turf backing.

LIST OF REFERENCE NUMERALS

-   -   102-104 steps     -   202 first tank for first mixture     -   204 second tank for second mixture     -   206 container for third mixture     -   208 blender     -   210 PU mass     -   210′ solidified PU mass     -   212 hose of coating assembly     -   214 opening of hose     -   302 fibers protruding from carrier     -   304 knife     -   306 roll     -   308 carrier, e.g. textile mesh     -   400 polymer mixture for fiber creation     -   402 hydrophobic fiber polymer     -   404 additive     -   406 additive     -   408 plate     -   410 opening of extrusion nozzle     -   412 extruded monofilament     -   501 artificial turf fiber     -   502 cutting operation     -   503 fiber loop     -   504 fiber portion within carrier     -   506 fiber portion protruding to the back side of the carrier     -   600 artificial turf     -   602 fiber portion protruding to the front side of the carrier         being embedded in the PU mass     -   604 fiber portion protruding to the front side of the carrier         not being embedded in the PU mass 

The invention claimed is:
 1. An artificial turf, comprising: a polyurethane backing formed from a non-foamed liquid polyurethane mass, the non-foamed liquid polyurethane mass being a reaction product of first and second polyols with an isocyanate, the first polyol being a polyether polyol and/or a polyester polyol having at least 2 hydroxyl groups per molecule, the second polyol being polybutadiendiol, and the isocyanate including isocyanate monomers, isocyanate polymers, or isocyanate prepolymers, or a mixture thereof, the isocyanate monomers, the isocyanate polymers, and the isocyanate prepolymers having two or more isocyanate groups per molecule; a carrier; and an artificial turf fiber incorporated into the carrier such that a first portion of the artificial turf fiber protrudes to a front side of the carrier and that a second portion of the artificial turf fiber is located at a back side of the carrier, at least the second portion of the artificial turf fiber being incorporated into the polyurethane backing, wherein the polybutadiendiol has an amount of 4.0-8.0% by weight of a combination of the first polyol and the isocyanate, wherein the carrier includes perforations, wherein the polyurethane backing is positioned on the back side of the carrier, in the perforations of the carrier and on the front side of the carrier, and wherein at least a portion of the first portion of the artificial turf fiber is incorporated into the polyurethane backing.
 2. The artificial turf of claim 1, wherein the artificial turf is manufactured based on creating the non-foamed liquid polyurethane mass, the creating including reacting the first and second polyols with the isocyanate; incorporating the artificial turf fiber into the carrier such that the first portion of the artificial turf fiber protrudes to the front side of the carrier and that the second portion of the artificial turf fiber is located at the back side of the carrier; adding the non-foamed liquid polyurethane mass on the back side of the carrier, the non-foamed liquid polyurethane mass thereby incorporating at least the second portion of the artificial turf fiber; and hardening the non-foamed liquid polyurethane mass on the back side of the carrier.
 3. The artificial turf of claim 2, wherein the non-foamed liquid polyurethane mass has a density of more than 1000 g/l. 